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<script>

class E{

	constructor(){
		this.a = new Set(["a","b","c","d"]);
	}

	test(){
	
		let that = this;
		this.a.forEach(function(v){
			if(v=="b"){
				that.a.delete(v);
			}
			
		})
		console.log("over>>",this.a);
	}

}


(new E()).test();



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